In bioreactors, which have a stirrer, it is necessary to optimally design and precisely install the stirrer, which has a stirring element arranged on a stirrer shaft. One particular aspect during installation is the precise setting of the angle of inclination, i.e., the angle of attack of the stirring blades that are to be arranged on a stirring blade receptacle. Since, when stirring, the highest angular speed may be found at the stirring blades of the stirrer, the highest shear forces are also at the stirring blades. If the angles deviate, then the shear forces rise dramatically, a phenomenon that results in injury to the organisms that are to be cultivated. In particular, in the case of reusable bioreactors, it is always necessary to remove the stirring elements when cleaning and then to install them again on the stirrer shaft. The ensuing process of adjusting the angle of attack has been a difficult, time-consuming and cost-intensive process to date.
The data sheet of Sartorius Stedim Biotech GmbH “Manual adjustment of 3-blade segment impeller to an angle of 30°” discloses a method for adjusting stirring blades in a stirring blade receptacle. The first step in this method is to screw the stirring blade only slightly into a threaded bore of the stirring blade receptacle by hand with a screwdriver. Then the desired attack angle of the stirring blade is set with an angle encoder; and the stirring blade is aligned along the angle-indicating device in such a way that the stirring blade receptacle is aligned parallel to the angle encoder. Only then is the stirring blade screwed firmly into the desired position in the threaded bore. The procedure is repeated sequentially for the other stirring blades. When all of the stirring blades have been screwed into the stirring blade receptacle at the required angle, the last step is to check, by placing the completely assembled stirring blade receptacle with the stirring blades on a flat surface, whether the underside of the stirring blade receptacle is aligned parallel to the flat surface, as a result of which it is ensured that all of the stirring blades are aligned at the desired angle of attack relative to the stirring blade receptacle.
The drawback with this procedure is that the adjustment is relatively time-consuming and, therefore, cost-intensive. In addition, the adjustment is relatively inaccurate.
DE 10 2006 053 339 A1 discloses a stirring device for fermenters, where in this case the stirring blades can be connected to a stirring blade receptacle, which is secured on a stirring shaft or more specifically on an axis of rotation, with a releasable plug-in connection. The end of a stirring blade that faces the stirring blade receptacle has a plug-in pin, which can be secured in a plug-in pin receptacle of the stirring blade receptacle with a locating screw in such a way that the plug-in pin can be released. The angle of attack of the stirring blades with respect to the axis of rotation can be varied by loosening, rotating and securing again the plug-in pin in the plug-in pin receptacle. In this case an angle of 5 to 15°, which is enclosed between the stirring blade longitudinal axis and the horizontal plane perpendicular to the axis of the stirrer shaft, remains constant in each instance. The end of the plug-in pin may be provided with, for example, four locking elements, which engage with four complementary locking receptacles on the end face of the plug-in pin receptacle. In this embodiment four different attack angles of the blades can be realized with respect to the stirrer hub. As an alternative, the plug-in pin may have a polygonal structure and may engage with a plug-in pin receptacle with a complementary polygonal receiving channel. In this embodiment it is possible to realize as many different angles of attack as there are corners on the polygonal structure.
The drawback with this known device is that it is, in particular, relatively cost-intensive to manufacture the stirring blade receptacle.
DE 27 02 795 C2 discloses an attachment for an angle-adjustable mixing blade on a support arm, which is fastened to a shaft, with at least one screw and nut connection and with at least one screw hole in the mixing blade, wherein the screw hole axis lies in a plane perpendicular to the support arm axis. The support arm has at least one oblong hole, which extends in a plane perpendicular to the support arm axis, and, parallel to the axis of the oblong hole, detent grooves, with which detents of the mixing blade engage. The attack angle of the mixing blade is varied by loosening the screw and nut connection, then lifting the detents out of the detent grooves and adjusting the mixing blade by rotating the mixing blade on a rounded engagement face of the support arm, so that the threaded bolts of the screws slide within the oblong holes.
The drawback with this device known from the prior art is also that it is, in particular, relatively cost-intensive to manufacture the stirring blade receptacle.
Furthermore, DE 197 11 019 A1 discloses a stirrer with stirring blades having angles of attack that can be variably changed for the purpose of carrying out polymerization reactions. In this case there are two stirring blades, which are mounted on a hollow drive shaft with two arms that are encapsulated. The stirring blades exhibit angles of inclination that can be varied relative to each other and with respect to the stirring shaft via a stoppable control shaft, which is located in the interior of the hollow drive shaft. The control shaft is connected to both arms through a toothed gear.
An important drawback with this device is that the stirrer is designed, on the whole, to be relatively complex and relatively cost-intensive.